1. Technical Field
This application relates to a catheter and more particularly to a multi-lumen catheter which facilitates hemodialysis.
2. Background of Related Art
Hemodialysis is a well known method of providing renal (kidney) function by circulating blood. The kidneys are organs which function to extract water and urea, mineral salts, toxins, and other waste products from the blood with filtering units called nephrons. From the nephrons the collected waste is sent to the bladder for excretion. For patients having one or both defective kidneys, the hemodialysis procedure is life saving because it provides a machine to simulate the function of the kidneys.
In the hemodialysis procedure, blood is withdrawn from the patient's body through a catheter or tube and transported to a dialysis machine, also commonly referred to as a kidney machine. The catheter is typically inserted through the jugular vein and maneuvered into position through the superior vena cava into the right atrium to provide high blood flow. In the dialysis machine, toxins and other waste products diffuse through a semi-permeable membrane into a dialysis fluid closely matching the chemical composition of the blood. The filtered blood, i.e. with the waste products removed, is then returned to the patient's body. In some instances, the catheter may be left in place for several years. As can be appreciated, proper access to the patient's blood and transport of the blood to and from the dialysis machine for this extended period of time is critical to hemodialysis.
One example of a dialysis catheter currently being marketed is the MedComp Ash Split catheter. This catheter has two lumens, one for arterial flow and the other for venous flow, which are each D-shaped in cross-sectional configuration. The catheter is bifurcated at its distal end to separate the lumens and the catheter is manually split to the desired length for selected separation before insertion into the target area. Another well-known catheter is a Med Comp catheter which has the venous flow lumen terminating proximally, i.e., axially recessed, from the arterial flow lumen. Each of these lumens is also D-shaped in cross-sectional configuration.
These Medcomp dialysis catheters require numerous steps for insertion. The multiple insertion steps can be summarized as follows:                1. an introducer needle is inserted through a first incision site (first opening) to properly locate (access) the vessel, e.g. the right internal jugular vein;        2. a guide wire is inserted through the needle into the internal jugular vein and down through the superior vena cava into the inferior vena cava;        3. the introducer needle is withdrawn leaving the guidewire in place;        4. a tear away (peel away) sheath and dilator are inserted over the guidewire and through the first incision site to provide an access port for the dialysis catheter into the jugular vein, superior vena cava and right atrium;        5. a second incision is made in the chest wall to create a second opening;        6. a trocar is attached to the distal end of the dialysis catheter;        7. the trocar and dialysis catheter are pushed through the second incision and advanced to bluntly dissect the subcutaneous tissue to exit the first incision (opening) which was created by the introducer needle, thereby creating a subcutaneous tissue tunnel between the first and second openings;        8. the trocar is detached from the dialysis catheter leaving the catheter in place extending from the second opening, through the tissue tunnel and out the first opening;        9. the dilator and guidewire are removed, leaving the tear away sheath in place in the first incision which has been expanded by the dilator;        10. the dialysis catheter, which is protruding from the first incision, is inserted through the tear away sheath and advanced so its distal portion is positioned in the right atrium;        11. the sheath is separated, i.e. split, by pulling the tabs apart, and then pulled upwardly away from the dialysis catheter and removed from the body, leaving the catheter in place; and        12. the second incision is closed and the dialysis catheter, which is connected through tubes to the dialysis machine, is left in place an extended period of time to provide blood circulation to and from the dialysis machine.        
(Alternatively, in the foregoing method, the trocar can be forced through a third incision exiting adjacent the first incision, and then the catheter inserted through second and third incisions and through the introducer sheath positioned in the first incision.)
This multiple step process of inserting the Medcomp dialysis catheter is time consuming and complicates the surgical procedure. These multiple steps add to the cost of the procedure, not only because of the additional surgeon's time but because additional components, such as the tear-away sheath, are required which increases the overall cost of the catheter system. Also, removal of the dilator increases the tendency of the sheath to kink causing difficulties in catheter insertion.
The use of the tear away sheath is also potentially problematic. The tear-away sheath has lines of weakness to separate it as it is pulled apart by the pull tabs to enable removal of the sheath. However, the sheath can potentially cause damage to the vessel wall as it is being pulled apart and can cause infection. Moreover, pulling the sheath laterally can enlarge the incision, thereby increasing the difficulty of closing the incision at the end of the procedure. Also, since the sheath is pulled in the proximal direction for removal, it could pull the catheter proximally as well, thereby pulling it away from the desired site, and requiring repositioning. The edges of the tear away can also lacerate the surgeon's glove and finger. Over dilation by the sheath can cause blood leakage.
An additional potential risk with utilizing tear away sheaths is that air embolism can occur. During the time the surgeon withdraws the dilator from the sheath and inserts the catheter, a passageway through the sheath to the vessel is open. If the patient inhales during this catheter exchange, an air bubble can enter the vascular system and obstruct the vessel, potentially causing stroke or even death.
It would therefore be advantageous if a dialysis catheter insertion method could be provided which reduces some of the foregoing procedural steps, thereby decreasing the complexity of the procedure and decreasing the hospital and surgeon costs. It would also be advantageous if such dialysis catheter insertion method could be provided which would be less traumatic and avoid the foregoing problems associated with the use of a tear-away sheath, such as increased risk of air embolism, trauma to the vessel wall, incision enlargement and dislodgement of the catheter.
Another area of dialysis catheter insertion, which needs improvement, is guiding the catheter to the target site. Dialysis catheters are composed of flexible tubing to minimize damage to the vessel wall during insertion and use. This flexibility, however, oftentimes results in kinking of the catheter since the catheter must navigate curves to reach the target vessel. This kinking can adversely affect blood flow. Also, the catheter needs to have some degree of stiffness to enable directing the catheter around the curves of the vessels. The stiffness, however provides its own risks since if the catheter is not properly directed, the catheter can inadvertently be forced against the vessel wall, thereby puncturing or damaging the vessel. Several different approaches have been discussed in the prior art to increase stiffness of catheters such as providing a distal tip of stiffer material to guide the catheter as in U.S. Pat. No. 5,957,893, using materials of different durometers in various portions of the catheter (U.S. Pat. No. 5,348,536), placing an additional concentration of material in the tip as in U.S. Pat. No. 4,583,968, or providing reinforcing strips, obturators or tubes within the catheter body to increase the rigidity (e.g. U.S. Pat. Nos. 4,619,643, 4,950,259, 5,221,255, 5,221,256, and 5,246,430). The need however exists to improve the balance between flexibility and stiffness. Thus it would be advantageous to provide a catheter with sufficient flexibility to accommodate anatomical curves of the patient while still having sufficient stiffness to enable guiding the flexible catheter tubing atraumatically through the length of the vessels.
In navigating vessels to access the target site, such as the right atrium, it is desirable to provide the smallest catheter profile, i.e. the smallest outer diameter catheter body. This profile facilitates insertion through smaller vessels as it reduces the likelihood of the catheter engaging the wall of the vessel and reduces trauma to the vessel by minimizing frictional contact with the vessel wall. However, the desire for smaller diameter catheters must be balanced against the need for providing sufficient sized lumens to enable proper blood flow. If the lumens are too small, sufficient blood flow may not be able to be maintained and the blood can be damaged during transport. Also, a sufficient relationship must be maintained between the size of the lumens and the overall diameter of the catheter to maintain the structural integrity of the catheter.
Numerous attempts have been made in the prior art to optimize the multi-lumen configuration. In some approaches, such as disclosed in U.S. Pat. Nos. 4,568,329 and 5,053,023, inflow and outflow lumen are provided side by side in D-shaped form. In other approaches, such as those disclosed in U.S. Pat. Nos. 4,493,696, 5,167,623 and 5,380,276 the inflow and outflow tubes are placed in concentric relation. Other examples of different lumen configurations are disclosed in U.S. Pat. Nos. 5,221,256, 5,364,344, and 5,451,206. The lumen configuration must accommodate two competing factors: keeping the catheter as small as possible to facilitate insertion while keeping the lumens as large as possible for blood flow. This balance must be achieved while maintaining the structural integrity of the catheter. It would therefore be advantageous to provide a catheter which reaches an optimum compromise between these two competing factors.
Another important feature of dialysis catheters is the suction openings to withdraw blood. Keeping the suction openings clear of thrombolytic material and away from the vessel wall is clearly essential to dialysis function since an adequate supply of blood must be removed from the patient to be dialyzed. However, a problem with prior dialysis catheters is that during blood withdrawal, as suction is being applied through the catheter openings and lumen, the suction can cause the catheter to be forced against the side wall of the vessel, known as “side port occlusion”, which can block the opening and adversely affect the function of the catheter by enabling only intermittent suction. In fact, the opening can become completely blocked, thereby preventing necessary intake of blood, i.e. venous flow. Fibrin sheath growth around the outside of the catheter can occur since dialysis catheters are oftentimes implanted for several months or even years. This fibrin growth, caused by the body's attempt to reject the catheter as a foreign body, could result in blocking of the suction holes.
The need therefore exists for an improved dialysis catheter which facilitates the surgical dialysis procedure. Such catheter would advantageously reduce the catheter insertion time, simplify the catheter insertion process, eliminate the need for a peel-away introducer sheath, decrease the chances of infection, reduce unwanted kinking of the catheter during insertion, strike an optimal balance between overall catheter and lumen size, and improve the suction capability to avoid hampering of blood flow.
Co-pending, commonly assigned prior patent application Ser. No. 10/025,506, filed Dec. 19, 2001, incorporated herein in by reference in its entirety, overcomes the disadvantages and deficiencies of the prior art. The dialysis catheter disclosed herein is a modification to the catheter of the '506 patent and provides similar advantages over the prior art.